DIESEL ALTITUDE ADJUSTMENT ADJ. TO IMPROVE PERFORMANCE

1983 6000 models equipped with 4.3L V-6 diesel engines will be manufactured with either high or low altitude diesel emission systems. Cars equipped with the high altitude emission system will be invoiced with option NA6. The type of system can also be identified by the emission label attached to the fan shroud. The use at either high or low altitude. These procedures are considered altitude performance adjustments and apply only to in-use vehicles. They should not be used to modify vehicles prior to sale.

CONVERSION OF LOW ALTITUDE SYSTEM TO HIGH ALTITUDE

Dealers in high altitude areas should encourage owners who have moved to high altitude counties to purchase the following adjustment procedure. This adjustment is considered an owner maintenance expense. See map (Figure 1) and list of counties (Figure 2 shown on the reverse side) which the Environmental Protection Agency has designated as high altitude counties. Diesel timing should be checked or adjusted at the same approximate altitude at which the vehicle will be driven.

1. Replace the EGR vacuum control valve (part number 22519396 or equivalent) with the assembly shown in the Parts Information section of this bulletin (see Figure 3 shown on the reverse side).

2. Remove and discard the vacuum modulator valve, if so equipped (refer to Figure 3).

3. Reroute the vacuum hoses as indicated in Figure 4 shown on page 3.

4. Install timing meter J-33075 or equivalent, set pump timing to -6 DEG, and set idle speed to specifications. Turn off engine.

5. Remove air crossover assembly. Install screen covers J-29657.

6. With transmission in Park and A/C off, start engine.

7. Loosen locknut (see Figure 5 on page 3) and slowly turn metering valve stop screw clockwise until idle speed drops approximately 10 RPM.

8. Turn metering valve stop screw counterclockwise 2 1/8 turns. Tighten locknut.

9. Check for fuel leaks around metering valve stop screw.

10. Turn engine off.

11. Remove magnetic tachometer probe and screened covers from intake manifold and reinstall air crossover and air cleaner.

12. Fill in dealer code and date on the supplemental emission control label, part number 14057201 or equivalent (see Figure 6 below). This label must be placed next to the existing underhood emission control information label. Wash off the area with soap and water, dry thoroughly, and apply the new label.

PARTS INFORMATION

PART PART NUMBER

1. EGR Vacuum Control Valve Assembly 22519396 or equivalent High Altitude Application

2. Label 14057201 or equivalent

Suggested Time

The suggested time to perform the High Altitude Adjustment and part replacement is 0.8 hour labor.

CONVERSION OF HIGH ALTITUDE SYSTEM TO LOW ALTITUDE

Dealers should advise owners moving to low altitude areas that they should purchase the following altitude adjustment procedure. This adjustment is considered an owner maintenance expense. Diesel timing should be checked or adjusted at the same approximate altitude at which the vehicle will be driven.

1. Replace the EGR valve vacuum control valve and vacuum modulator valve with the assemblies listed in the Parts Information section of this bulletin.

2. Install a vacuum modulator valve, part number 563494 or equivalent, in the location as shown in Figure 3. A rubber block connector, "F" connector, and elbow connector will also be required to convert to the low altitude system as shown in Figure 3. Additional vacuum hose may also be required. The part numbers for all parts required are listed in the Parts Information section of this bulletin.

3. Reroute the vacuum hoses and install the above parts as indicated (refer to Figure 3 shown on page 2).

4. Install timing meter J-33075 or equivalent, set pump timing to -6 DEG, and set idle speed to specifications. Turn off engine.

5. Remove air crossover assembly. Install screen covers J-29657.

6. Loosen lock nut (refer to Figure 5 shown on page 3) and turn metering valve stop screw counterclockwise 1 1/2 turns. Tighten lock nut.

7. Start engine. With engine running and transmission in Park, check for fuel leaks around metering valve stop screw. Turn engine off.

8. Remove magnetic tachometer probe and screened covers from intake manifold and reinstall air crossover and air cleaner.

9. Fill in dealer code and date on the supplemental emission control label, part number 14055121 or equivalent (see Figure 7 shown on the following page). The label must be placed next to the existing underhood emission control information label. Wash off the area with soap and water, dry thoroughly and apply the new label.

PARTS INFORMATION PART PART NUMBER

1. EGR Vacuum Control Valve Assembly 22519395 or equivalent Low Altitude Application 2. Vacuum Modulator Valve 563494 or equivalent 3. "F" Connector 22502326 or equivalent 4. Elbow Connector 556992 or equivalent 5. Rubber Block Connector 560840 or equivalent 6. Vacuum Hose (Bulk) 9438381 or equivalent 7. Label 14055121 or equivalent

Suggested Time

The suggested time to perform High to Low Altitude adjustment and part replacement is 0.8 hour labor.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.